A few captured Frenchman in battle (5)
I believe the answer is:
somme
'battle' is the definition.
(Battle of the Somme in WW1)
'a few captured frenchman' is the wordplay.
'a few' becomes 'some' (both can mean a small amount of something).
'captured' indicates putting letters inside.
'frenchman' becomes 'm' (abbreviation for Monsieur).
'some' going around 'm' is 'SOMME'.
'in' acts as a link.
(Other definitions for somme that I've seen before include "World War One battle region" , "World War I battlefield around French river" , "World War one battle where great losses were incurred" , "WWI battle site" , "WW1 battle site" .)